In the electric power generating industry, nuclear powered electric generating plants are a potential source of a number of types of radioactively contaminated materials in addition to the fuel elements of a nuclear reactor and the primary materials in contact therewith. All such materials must be handled and disposed of in a manner consistent with both current technology and existing law.
One type of secondary materials which may become radioactively contaminated even though not in direct communication or contact with nuclear fuel or other high radiation elements, are the ordinary lubricating oils used in all types of machinery in many different applications and which are not necessarily specific to the nuclear industry. Usually the machinery in which such contaminated oil might be found is that which contains or pumps water or water solutions of various chemicals.
In the normal operation of such machinery, whether in nuclear powered electric generating plants, other types of generating plants, or totally unrelated industries, a common occurrence is the almost inevitable mixture of some amount of the lubricating oil used in the machinery with the water or other fluid which the machinery holds, transfers or pumps. Even in non-nuclear conventional industries, the effects of such mixtures must eventually be dealt with, usually by replacing or recycling the oil. Additionally, all lubricating oils have some limited operating lifetime, after which they must be replaced whether or not contaminated with other fluids.
In a nuclear powered electric generating plant, however, special problems arise. Because there are some pumps and other machinery in a nuclear power plant which must circulate coolant (usually water contaminated with radioactive corrosion products) within or closely adjacent the reactor vessel, the potential will always exist that some amount of radioactivity will be present in the water being handled or pumped. Consequently, any of this water which mixes with the lubricating oil in the machinery will radioactively contaminate the oil.
Most of the radioactive elements of more than minimal half-life are metals. The radioactive isotopes of such metals are often referred to as radionuclides and such will be the use of the word herein. The radionuclides most often encountered in waste lubricating oil are Mn-54, Co-58, Co-60, Cs-134 and Cs-137. In a nuclear powered electric generating plant these radionuclides are generally present due to minor defects in fuel cladding, neutron activation and small amounts of particulate matter introduced during the operation of the machinery or the transfer and storage of the oil.
Although the radioactivity levels in the waste lubricating oil from a nuclear powered plant are generally quite low--indeed lower than much naturally occurring radioactivity in everyday surroundings--because they are "man-made" isotopes, the law requires that they be classified as low level waste. Normally low level radioactive waste can be disposed of by shallow land burial, however, state and federal regulations prohibit the burial of radioactive liquids. Additionally, there is no state or federal law or regulation which defines a de minimus standard for waste lubricating oil. Thus, no matter how well waste lubricating oil is decontaminated, it must still be classified as low level waste and disposed of according to law.
Because of the lack of de minimus standards and the prohibition against burial of radioactive liquids, the operating utilities either solidify or absorb the oil in one of a variety of media and then bury the media in 55 gallon drums. This procedure is inefficient, uses tremendous amounts of space and is very expensive. Typically, only ten or twelve gallons of oil can be placed in each 55 gallon drum. At 1985 prices, disposing of such oil costs between $500 and $1200 per drum. This reflects not only the cost of solidifying the oil but also the intermediate handling and transportation of such drums to the single waste disposal site available for them in the United States. Currently there are 115 nuclear power plants in the United States, producing between 5,000 and 10,000 gallons per year of such waste oil, so that the problem represents a $20,000,000 to $60,000,000 per year industry wide economic problem.
Relatively few attempts have been made to decontaminate waste lubricating oil formed at nuclear power plants. Most of this work has focused on physical means of treatment such as filtration and separation. Particular studies have dealt with ultrafiltration (filtration on a molecular level) and treatment with mixtures of other materials such as acids and clays. Although these earlier methods represent legitimate separation techniques, they are all premised on the assumption that the decontamination of waste lubricating oil must be accomplished by separating the contaminated water from the oil, after which the oil would be decontaminated. In practice, however, merely separating the oil from the water, no matter how completely or efficiently, does not result in decontaminated lubricating oil and consequently such methods have been found to be unsatisfactory as ultimate disposal methods. Additionally, some of these methods are rather sophisticated and difficult to accomplish even in laboratories. Consequently they are unattractive for use on the scale necessary to address the industry-wide problem.
In developing the present invention, it has been discovered that the contaminated radioactivity, however, includes an organic component. It will thus be seen that the need exists for providing a means of dealing with the organic contaminants in waste lubricating oil and in addition attempting to merely dispose of the water-soluble inorganic component.
It is thus an object of the present invention to provide a method of decontaminating waste lubricating oil which eliminates the need for dispersing such oil into some solid medium, storing the dispersed oil in drums and shipping the drums long distances to a single disposal site.
It is a further object of this invention to provide a method of decontaminating waste lubricating oils so that the resulting decontaminated oil can be disposed of in a conventional manner, such as by combustion.
It is another object of this invention to provide a method of decontaminating waste lubricating oil which is technologically straightforward, uses existing production scale equipment and can treat large and small amounts of material in an equally beneficial fashion.
Finally, it is an object of this invention to provide a method of decontaminating both emulsions of aqueous solutions and contaminated waste lubricating oil and mixtures of particulate material with such emulsions such that the aqueous portions and the organic portions of such emulsions can both be ultimately disposed of in conventional manners rather than by storage in inefficient and expensive hazardous waste disposal sites.